1. Field of the Invention
The present invention relates to a sheet processing apparatus which performs a binding process on sheets fed from an image forming apparatus, and relates to improvement of a binding processing mechanism to perform a binding process as collating and stacking image-formed sheets and selecting one of different binding processing devices.
2. Description of Related Arts
In general, there has been known a sheet binding processing apparatus in which sheets image-formed at an image forming apparatus are collated and stacked on a processing tray after being guided from a sheet introducing path, a binding process using a staple is performed on the sheets which are formed into a sheet bundle, and the bound sheet bundle is stacked on a stack tray.
Such sheet binding processing apparatuses are categorized into a sheet bundle moving type with which a binding process is performed after a stacked sheet bundle is moved to a binding processing position of a binding processing unit and a unit moving type with which a binding process is performed after a binding processing unit is moved to a predetermined position of a stacked sheet bundle. Here, the sheet bundle moving type has following problems and the like.    (1) A sheet bundle is easy to be disarranged in posture when being moved and appearance of a processed sheet bundle becomes worse owing to that a binding process is performed in a state of disarranged posture.    (2) The apparatus is upsized as a whole owing to a space required for moving a whole sheet bundle.
Accordingly, sheet binding processing apparatuses of the unit moving type have been widely used in the market.
Meanwhile, recently, it has been desired in the market for a sheet binding processing apparatus in which a plurality of binding processing units is used separately. For example, there has been newly known a sheet binding processing apparatus which adopts a so-called non-stapling unit to perform a binding process on a sheet bundle with a method such as applying high pressure onto the sheet bundle without using a staple as well as to perform a binding process on a sheet bundle using a staple.
Japanese Patent Application Laid-open No. 2012-027118 discloses such a new sheet binding processing apparatus of the unit moving type in which both of a stapling unit and a non-stapling unit are arranged movably against a sheet bundle stacked on a processing tray and a binding process is to be performed at a predetermined binding position.
In the apparatus disclosed in Japanese Patent Application Laid-open No. 2012-027118, each unit is moved to the predetermined binding position to perform a binding process in a state that an end edge of a sheet bundle is introduced to an opening portion of the stapling unit and an opening portion of the non-stapling unit.
Accordingly, there has been a problem that a sheet bundle is disarranged in posture owing to that sheets interfere with an opening portion of one unit when a binding process is to be performed on the sheet bundle by the other unit.
In particular, in a case that a binding processing unit having a low binding processing capacity and a narrow opening portion is included in a plurality of binding processing units, the problem such as sheet bundle disarrangement appears notably. Further, in a case that differences exist among processing capacities of the binding processing units, there has been a problem that an expected processing capacity cannot be obtained owing to that the number of sheets to be processed by a binding processing unit having a high processing capacity with respect to the number of sheets to be processed is limited to the number of sheets to be processed by a binding processing unit having a low binding processing capacity.